Spinning of viscose



United States Patent 3,531,560 SPINNING 0F VISCOSE Donald M. MacDonald, Hawkesbury, Ontario, and Edgardo J. Alvarez, St. Foy, Quebec, Canada, assignors to Canadian International Paper Company, Montreal, Quebec, Canada, a corporation of Canada No Drawing. Filed Oct. 28, 1968, Ser. No. 771,282 Int. Cl. D01f 3/12 US. Cl. 264-189 6 Claims ABSTRACT OF THE DISCLOSURE In the manufacture of rayon by the viscose process, the incorporation in a zinc-free spinbath of a tertiary monoamine hydrating agent having a minimum of three and a maximum of nine carbon atoms and a maximum of four carbon atoms in any single radical and wherein at least one of the radicals is a single carbon radical with one hydroxyl radical bonded thereto, has been found to produce a low elongation rayon filament having improved strength and Wet modulus properties.

This invention relates to the manufacture of regenerated cellulosic structures by the viscose process. More particularly, it relates to an improved process for spinning a viscose solution into an aqueous spinbath solution containing a viscose hydrating agent whereby a high strength rayon filament is regenerated.

The production of regenerated cellulosic structures, i.e., rayon filaments, by the viscose process typically involves as an initial step the conversion of a cellulosic material to alkali cellulose by treatment with caustic soda. The alkali cellulose is then shredded and allowed to age. Subsequent to the aging step, the alkali cellulose is converted to cellulose xanthate by treatment with carbon disulfide. The xanthated cellulose is then dissolved in a caustic soda solution to provide a viscose having the desired cellulose and alkali content. The viscose solution, subsequent to filtration, is allowed to ripen and is then extruded through a spinnerette into a spinbath, which serves as a coagulating-regenerating bath.

The spinbath consists of an aqueous acid solution, and it also typically contains zinc sulfate, or some other zinc or metal salt. The zinc sulfate acts as a regeneration retardant by forming zinc xanthate salts in the filament which results in dehydration of the filament. In addition, viscose modifiers, exemplary of which are polyethylene oxide, certain amines, carbamates, etc., have been used in conjunction with the zinc sulfate as auxiliary regeneration retardants. After passing from the spinbath the filaments can then be passed into a second bath, commonly referred to as a stretch bath, which is a hot aqueous bath, Where the filaments are stretched to improve their strength properties. The filaments can then be passed into a third bath to complete regeneration of the cellulose, if regeneration has not been completed upon exiting from the stretch bath. The filaments are then, typically, washed, bleached, and dried.

However, the highly prevalent use of zinc sulfatein the viscose process has certain notable disadvantages. It is very expensive; for high strength rayons such as tire yarns or high wet modulus yarns the modifiers previously adverted to must be employed in conjunction with it, and it also has, to a certain degree, the tendency to form encrusting deposits on the spinning equipment.

Heretofore, it was thought desirable, at least in certain commercial applications, and in particular those directed to obtaining a high wet modulus rayon, to promote a hydration or water retention effect in a spinning viscose filament, as opposed to the conventional dehy- 3,531,560 Patented Sept. 29, 1970 ICC drating effect. This obviated the need for employing zinc salts and viscose modifiers in the spinbath. Formaldehyde, for example, was shown to promote hydration of a spinning viscose filament, as measured by high values found in the gel swelling test, while still achieving a fila- =ment having a high degree of stretchability.

Commercial production of rayons using formaldehyde has, however, not become widespread commercially because of certain manufacturing difiiculties. The most notable disadvantage associated with the use of formaldehyde is the formation of crusts on the spinnerette and other spinbath equipment, i.e., the piping. These crusts are hard, crystalline deposits. With continued spinning, these deposits build up and eventually clog and foul the spinnerette and the piping. These deposits are composed of trithiane or 1-hydroxy-2-oxa-4, 6-dithioheptane-7-thiol or a mixture of the two, possibly accompanied by a polymer of the latter compound. In addition, formaldehyde has an extremely disagreeable vapor necessitating the use of special ventilating equipment. Even with the use of special ventilating equipment, pollution of the atmosphere poses a serious problem. Also, the formaldehyde contained in the spent acid is volatile in the recovery boilers where excess water is boiled off and excess sodium sulphate is crystallized. Thus, the use of formaldehyde as a hydrating agent or additive in the spinbath has proven economically disadvantageous.

Therefore, it is an object of the present invention to provide a viscose manufacturing process and a spinbath solution for use in said process which promotes filament hydration in a manner similar to that of formaldehyde, but without the disadvantages associated with formaldehyde, namely fouling of the spinnerette or spinbath piping with crystalline deposits, the emission of disagreeable vapors and associated adverse physiological effects, and excessive volatility.

It is another object of the present invention to provide a process and a spinbath solution which eliminates the necessity for adding expensive zinc salts to the spinbath.

It is another object of the present invention to provide a rayon spinning process and a hydrating agent for use therewith in a zinc-free aqueous spinbath solution, which results in an economical process for the production of a high wet modulus, high strength, low elongation rayon filament.

It has been found that certain monoamines promote a hydration or water retention effect in the spinning viscose filament. Monoamines which have been found to promote this water retention effect are tertiary monoamines having the formula wherein R and R are selected from the group consisting of methyl, ethyl, propyl, isopropyl and butyl radicals. The tertiary monoamines of the present invention enhance the hydration of the viscose filaments, thus producing regenerated cellulosic structures, e.g., rayon filaments, having high stretchability and, thus, improved strength. Exemplary of these tertiary monoamines are: methylol dimethylamine, methylol methylethylamine, methylol methylpropylamine, methylol methylisopropylamine, methylol methylbutylarnine, methylol diethylamine, methylol ethylpropylamine, methylol ethylisopropylamine, methylol ethylbutylamine, methylol dipropylamine, methylol propylisopropylamine, methylol propylbutylamine, methylol diisopropylamine, methylol isoproylbutylamine and methylol dibutylamine. Methylol dimethylamine has been found to be preferred in the practice of the instant invention.

The hydrating action of the tertiary monoamines of the present invention appears to be a consequence of the stabilization of cellulose xanthate to the acidic spinbath by the formation of a derivative. The existence of the methylol dimethylamine-cellulose xanthate derivative, for example, has been confirmed by a comparison of its ultraviolet spectrum with the ultraviolet spectrum of sodium cellulose xanthate. When a thin film of sodium cellulose xanthate was exposed to ultraviolet light, the maximum light absorption occurred at 303 millimicrons. When methylol dimethylamine was reacted with cellulose xanthate, it produced a derivative having a maximum light absorption at 280 millimicrons. This indicates that the methylol dimethylamine forms a methylol dimethylaminecellulose xanthate derivative having the formula CellOCS CH N C 3 2 Typically, xanthate derivatives are somewhat unstable, as has been found by the lowering of light absorption with the passage of time. However, the tertiary monoamine xanthate derivatives are much more stable than a film of cellulose xanthate obtained from a spinbath Where no tertiary monoamine derivative-forming material is present. While these tertiary monoamine derivatives are sufiiciently insoluble in water to permit rayon spinning they retain much more water than the more regenerated yarn obtained from a cellulose xanthate wherein no tertiary monoamine hydrating agent is present. Thus, the derivative containing filaments are stabilized in a state which permits a high degree of hydration.

Viscosemodifiers, however, do not react with cellulose xanthate. Instead, they interact with the zinc of the zinc sulfate present in the spinbath and viscose by-products, mainly trithiocarbonate ion, to form a film on the filament surface which hinders acid penetration. The film allows water to pass out of the filament while delaying acid penetration. Consequently, a more dehydrated filament is obtained in the presence of a conventional modifier. The filament which is obtained cannot be stretched to the same degree during spinning as a filament obtained from a tertiary monoamine-xanthate derivative.

The high strength, low elongation rayon filaments obtained by the present invention can be used in (1) certain types of high or intermediate wet modulus rayons, (2) as reinforcing fibers for plastic composites, and (3) as tire cords in radial ply tires.

Strength improvement of the filaments, employing the tertiary monoamine hydrating agents of the present invention, is obtained if the viscose index is from about 1.5 to about or above, as measured by the classical salt test, and preferably about 16 or above. To achieve such an index, fairly high carbon disulfide levels, as discussed hereinafter, are necessary during xanthation. The viscosity of the viscose solution can be from about 15 to about 1,000 poises or above in order to obtain strength improvement. It is preferred that the viscosity be in the range of from about 150 to about 400 poises. In typical viscose processes, when conventional viscose modifiers are employed strength improvement is achieved when the viscose index is within the range of 3 to 12.

In the preparation of the viscose, the degree of polymerization of the cellulose xanthate can be from about 150 to about 1,200. The cellulose employed can be, for example, Multicell wood pulp, a prehydrolyzed kraft pulp of International Paper Company, or high-alpha cellulose pulps, dissolving pulps, cotton linters, cold-caustic refined pulp, resin-free pulp, etc. A degree of polymerization of from about 300 to about 500 is preferred.

A typical viscose composition for use in the practice of the present invention compirses 7.0% cellulose and 7.5% sodium hydroxide. However, the cellulose can be present in amounts of from about 6% to about 12% and the amount of sodium hydroxide can be from about 3% to about 9%.

It is preferred that the viscose solution have a salt index of about 16 or above and a viscosity of from about 150 to about 400 poises, as previously indicated. Accordingly, in order to achieve strength improvements the alkali cellulose is xanthated with from about 20% to about 100% of carbon disulfide, the percentage of carbon disulfide being based on the cellulose content of the alkali cellulose. It is preferred, however, to use from about 45% to about 55% carbon disulfide'. The xanthation is carried out by conventional techniques well-known in the art.

The tertiary monoamine hydrating agents can be added to the viscose solution, just prior to extrusion from the spinnerette or they can be incorporated directly into the spinbath solution. It is preferred to incorporate the tertiary monoamines directly into the spinbath solution. The composition of the aqueous spinbath solution, with functions as a coagulating-regenerating bath, comprises from about 0.1% to about 5.0% of the tertiary monoamine of the present invention, from about 2% to about 25% sulfuric acid and from about 4% to about 30% sodium sulfate. All percentages are based upon the weight of the spinbath solution. It is preferred to employ from about 0.4% to about 4.0% tertiary monoamine, from about 3.7% to about 5.5% sulfuric acid and from about 5.5% to about 10% sodium sulfate. The spinbath solution has no zinc salts present.

The spinning operation involves extruding the viscose solution through a spinnerette into the spinbath solution described above. The temperature of the aqueous spinbath solution is maintained at from about 20 C. to about C., preferably from about 25 C. to about 30 C. A spinning speed of 25 meters/minute is preferred, although greater or lesser speeds can be effectively employed.

After passing through the spinbath the filaments pass into an acidic stretch bath containing less than 1% zinc sulfate. The presence of zinc sulfate in the stretch bath is optional. It appears, however, to aid in the spinning operation. However, it should be understood, that the presence of zinc sulfate in the stretch bath is not necessary, since good results have been obtained when it was completely absent from the stretch bath. In fact, good results have been obtained when the stretch bath consisted only of water. The stretch bath is maintained at a temperature of from about 80 C. to about C.

It has been found that maximum filament strength is achieved when the filaments have been stretched to the point where few or no broken filaments occur. The degree of stretch capable of being imparted to a filament is to a large extent dependent on the concentration of the tertiary monoamine hydrating agent in the spinbath. Therefore, the degree of stretch can vary in our process from about at least to about 300% or more. It has been found that at stretch broken filaments are substantially absent.

After passing through the stretch bath the filaments can then, optionally, be passed into a third bath which is acidic in nature and which serves as a purifying bath. After passing out of the third bath the filaments are collected on a spool while still in the wet state.

The following examples are intended to be illustrative only and are not intended, in any fashion, to be limiting.

EXAMPLE 1 Methylol dimethylamine was prepared by mixing equimolar quantities of a 37% formaldehyde solution and a 25% dimethylamine solution. After mixing, the solution was adjusted to a pH of 3.0 by the addition of sulfuric acid. To prevent formaldehyde loss the temperature was maintained below 50 C. during the mixing period and during the pH adjustment.

EXAMPLE 2 Five separate batches of a viscose solution were prepared employing 7.0% Multicell wood pulp and 7.5 sodium hydroxide. Each viscose solution was xanthated with 50% carbon disulfide. The viscose index in each instance was 17.6, as measured by the classical salt test, and the viscosity was 250 poises. The viscose solutions were spun into spinbaths, the compositions of which are given in Table I below. The methylol dimethylamine used in batches 2-5, inclusive, was prepared in accordance with Example 1 above. Spinning was carried out at a speed of 25 meters/minute in baths which were maintained at 26 C. Each of the yarns after passing through their respective spinbaths passed into and through a stretch bath consisting of 15 g./l. of sulfuric acid and 8 g./l. of zinc sulfate. The stretch bath was maintained at 90 C. Maximum stretch was applied in each case.

TABLE I The filament traveled horizontally 11 inches to a guide and then one inch verticallybefore exiting from the bath, giving a total immersion of twelve inches. The composition of the spinbath was 45 g./l. sulfuric acid (4.1%), 70 g./l. sodium sulfate (6.4%) and 5.4 g./l. methylol dimethylamine (0.5%). The bath had a specific gravity of 1.088 and the temperature of the bath was maintained at 26 C. The filaments then passed into and through a second bath, commonly referred to as a stretch bath. The second bath had an immersion of thirty inches. The composition of the stretch bath was g./l. sulfuric acid (4.1%), 8 g./l. zinc sulfate (0.8%). The stretch bath had a specific gravity of 1.03 and the temperature Yarn properties Bath composition in g./l. Tenacity (g./d.)

Elongation (percent) Stretch Wet Wet modulus Conditioned About 1 gram/denier improvement in strength, both Wet and conditioned, was obtained by the addition of 5.4 g./l. of methylol dimethylamine to the spinbath, as is evident when batches 1 and 2 are compared. Batches 3, 4 and 5 show the results which can be obtained by varying the sulfuric acid and sodium sulfate levels in the bath while maintaining the amount of methylol dimethylamine constant. From the results shown in Table I it can be concluded that low salt levels are beneficial, while acid levels can be varied rather widely without any appreciable effect.

EXAMPLE 3 The yarn primary gel swelling of batches 1, 2 and 3 listed in Table I of Example 2 were compared after passing through the stretch bath and after washing.

The primary gel swellings were determined by cutting a short length of yarn at the appropriate position, washing the yarn free of acid and salts with water, removing excess water by centrifugation, weighing the sample after centrifugation, drying the sample and reweighing. Gel swelling is the ratio of the wet weight to the drywe ght and higher gel swelling demonstrates higher hydration.

It was attempted to measure the gel swellings after the spinbath; however, all the samples either dissolved on washing or had so jelly-like a consistency that they could not be centrifuged.

The values obtained after the stretch bath, as shown in Table II below, indicate distinctly higher primary swellings or hydration levels after stretching, but no difference after washing when the xanthate-methylol d1- methylamine derivative would be decomposed. These derivatives decompose spontaneously to cellulose xanthate and, subsequently, to cellulose upon the removal of acld. Batch numbers in Table II below refer to the same batch numbers as in Table I of Example 2.

TABLE II Yarn primary gel swelling after- Batch Stretch bath Washing EXAMPLE 4 of the bath was maintained at C. The filaments then passed into a third bath, which is a purifying bath. The third bath had an immersion of sixty inches. The composition of this bath was 60 g./l. of sulfuric acid and the temperature of the bath was maintained at 60 C. The filaments were then washed and collected in a wet state on a spool. The spinning speed was 25 meters/ minute. The filaments were stretchable to the extent of Another viscose, referred to as B in Table III below, which When prepared had a viscose index of 16.7 and a viscosity of 230 poises, was spun in the same bath and under the same conditions as was viscose A, except that no methylol dimethylamine was present in the spinbath. This B filament could be stretched only 157%.

The test results in Table III below, including the stretch values previously noted, indicate the improved results obtained by incorporating methylol dimethylamine in the spinbath.

Various alternatives and modifications will be appar ent to those skilled in the art upon a reading of the foregoing specification Without departing from the disclosed inventive concept.

What is claimed is:

1. A method of producing regenerated cellulosic structures which can be stretched from at least 1110% to about 300% or more having high strength and low elongation from a viscose solution having a salt index of from about 1.5 to about 20 or above and a viscosity of from about 15 to about 1000 poises or above which consists essentially of spinning the viscose solution into an aqueous spinbath solution at a temperature of from about 25 C. to about 30 C. having from about 2% to about 25% by weight of sulfuric acid and from about 4% to about 30% by weight of sodium sulfate and from about 0.1% to about 5% by weight of a tertiary monoamine having the formula wherein R and R are selected from the group consisting of methyl, ethyl, propyl, isopropyl and butyl.

2. The process as recited in claim 1 wherein said tertiary monoamine is methylol dimethylamine and comprises from about 0.4% to 4.0% by Weight of said spinbath solution.

3. The process as recited in claim 1 wherein said spin bath solution is free of zinc salts.

4. An aqueous spinbath solution for the spinning of regenerated cellulosic structures from viscose having a salt index of from about 1.5 to about 20 or above and a viscosity of from about 15 to about 1000 poises or above consisting essentially of from about 2% to about 25% by weight of sulfuric acid and from about 4% to about 30% by Weight of sodium sulfate and from about 0.1% to about 5% by weight of a tertiary monoamine having the formula I-CHzOH wherein R and R are selected from the group consisting of methyl, ethyl, propyl, isopropyl and butyl.

5. The spinbath solution as recited in claim 4 wherein said tertiary monoamine is methylol dimethylamine and comprises from about 0.4% to about 4.0% by weight of said spinbath solution.

6. The viscose spinbath solution as recited in claim 4 wherein said spinbath solution is free of zinc salts.

References Cited JULIUS FROME, Primary Examiner J. H. WOO, Assistant Examiner US. Cl. X.R. 264-188 

